1. Field of the Invention
The present invention relates to a method of stopping a movable die of an injection molding machine at its open side and to a die clamping apparatus.
2. Description of the Related Art
In a conventional injection molding machine, a resin heated and melted by a heating cylinder is charged into a cavity in a die. The molten resin is then cooled to obtain a molded product, which is taken out after opening the die.
The die is composed of a stationary die and a movable die which is disposed facing the stationary die and is guided for advancing and retracting movement. Die closing is effected by advancing the movable die and die clamping is effected by pressing the movable die against the stationary die, while die opening is effected by retracting the movable die. For this purpose, a die clamping apparatus is provided in the injection molding machine. The die clamping apparatus is composed of a stationary platen carrying the stationary die, a toggle support, a movable platen carrying the movable die, and a toggle mechanism for advancing and retracting the movable platen. The toggle support is supported by the stationary platen via tie bars, and the toggle mechanism is disposed between the movable platen and the toggle support. Accordingly, when the toggle mechanism is operated, the movable die is moved along the tie bars.
Also, a die clamping cylinder is disposed to operate the toggle mechanism. The die clamping cylinder comprises a piston so that fluid chambers are formed on both sides of the piston. By supplying the fluid chambers with working fluid, the piston is advanced to operate the toggle mechanism such that die closing and die clamping are successively effected, or the piston is retracted to reversely operate the toggle mechanism such that die opening is effected.
A mechanical stopper (stop position setting device) is provided in the clamping cylinder to restrict retracting movement of the piston. The mechanical stopper is used to set the most retracted position of the movable platen within the movable stroke (hereinafter referred to as a "die open-side stop position"). The movable platen is therefore stopped at the "die open-side stop position" during a retracting movement for die opening. The mechanical stopper also secures the accuracy of the stopping operation.
FIG. 1 is a sectional view of a conventional die clamping cylinder.
As shown in FIG. 1, a piston 12 is slidably received in a tubular die clamping cylinder 11 so that a pair of fluid chambers 13 and 14 are formed on the rear and front sides (the left and right sides as viewed in FIG. 1) of the piston 12. The fluid chambers 13 and 14 are provided with respective ports 16 and 17 through which working fluid is supplied to the fluid chambers 13 and 14. Also, a piston rod 18 is integrally formed with the piston 12, and an unillustrated toggle mechanism is connected to the piston rod 18.
Accordingly, when the piston 12 is advanced (to the right in FIG. 1) by supplying working fluid to the fluid chamber 13 through the port 16, the toggle mechanism is operated so that an unillustrated movable platen is advanced for die closing and die clamping. Also, when the piston 12 is retracted (to the left in FIG. 1) by supplying working fluid to the fluid chamber 14 through the port 17, the toggle mechanism is operated so that the movable platen is retracted for die opening.
A mechanical stopper 22 is disposed in the die clamping cylinder 11 at its left end as viewed in FIG. 1 so as to set a die open-side stop position where the movable platen is stopped during the retracting movement for die opening, and to guarantee the accuracy of the stopped position. The mechanical stopper 22 is composed of a tubular member having a female screw on its inner surface and an adjusting member is disposed therein. The adjusting member 23 having a male screw on its outer surface is screw-engaged with the mechanical stopper 22.
A handle 24 is attached to the adjusting member 23 at its rear end (at its left end as viewed in FIG. 1), which allows an operator to operate the handle 24 so as to rotate the adjusting member 23. A guide groove 26 extending in the axial direction of the cylinder 11 is formed in the outer surface of the mechanical stopper 22, and a pin 27 is engaged with the guide groove 26 for prohibiting rotational movement of the mechanical stopper 22. Accordingly, when the adjusting member 23 is rotated by operating the handle 24, the mechanical stopper 22 is reciprocated in the axial direction.
The mechanical stopper 22 has a front end surface (a right end surface as viewed in FIG. 1) which can be contacted with an abutting surface 29 of the piston 12. The mechanical stopper 22 is used to set the above-described die open-side stop position, i.e., the stroke end of the piston 12 during die opening, by restricting movement of the piston.
However it is necessary to rotate the adjusting member 23 by operating the handle for moving the mechanical stopper 22 when an operator tries to change the setting of the die open-side stop position.
And also to set the die open-side stop position automatically a motor, a feed mechanism, and the like must to be used, making the structure of the clamping apparatus complicated.
Moreover, if the die open-side stop position is set without the mechanical stopper 22 and a die opening speed is increased for shortening a molding cycle, the movable die would overrun after the die opening.
As a result it is possible to prevent the stop position of the movable die from varying in each molding cycle. So it is impossible to take out a molded product automatically by a device for taking out a molded product.